The Google booth at the RSA convention in San Francisco is shown Tuesday, April 8, 2008. Google Inc. reports earnings for the first quarter after the market closes on Thursday, April 17, 2008. (AP Photo/Paul Sakuma)

At its heart, Google Voice is a call forwarding service, providing a single number that can ring all, or any, of your phones.

But the Mountain View Internet company's vision is much more ambitious: to supplant the mishmash of passwords, formats and contact lists across office, home and mobile phones with a simple, one-stop platform, easily accessible anytime and anywhere.

"Google Voice is about helping you organize all your communications, whether it's calls or SMS, and have them all in one place in the cloud, tied to you, not to a device or location," said Vincent Paquet, senior product manager for Google Voice.

It almost does it, too.

For now, however, Google Voice's inventive and helpful features are layered atop existing devices, software and contracts, not seamlessly integrated. That leaves them subject to complications that prevent the service from fully realizing its promise.

Google Inc. introduced the tool, an upgrade of the GrandCentral product it acquired last year, in March. To use Voice, which is free except when making international calls, customers must sign up at www.google.com/voice and wait for an invitation that often takes weeks. The company isn't saying when it will make the service more widely available.

I received my invite early last month and have been using it since. Because I work from several offices and attend press events frequently, I was excited about the opportunity to easily forward calls to whatever phone happened to be closest to me on any given day.

Cool features

It's delivered on my hopes: I don't have to give out my cell phone number for work calls, leave drawn out call back instructions on voice messages, or miss a return call I critically need.

Other cool features abound.

I can send different callers to different phones, or direct strangers straight to voice mail. I can hit 4 during a call to record it (no small aid for a journalist with slow fingers).

Google Voice transcribes voice mails, which I can read online or have delivered as e-mails or texts. They're not perfect, but they're generally good enough to provide the gist.

I can personalize my voice mail greeting for different groups like friends or co-workers, or even for individuals.

I set up one for a good friend ("Sorry, I can't take your call right now, but I'm busy lying on the couch.") that was a little different from the one for my boss ("Sorry, I can't take your call right now, but I'm working very diligently to meet my deadline and exceed your expectations.").

Google Voice can also save money. International calls are cheap, checking voice mails or sending texts online slows the consumption of monthly carrier allotments, and making domestic long-distance calls through the service can sometimes be cheaper.

Frustrating elements

But for all its advantages, Google Voice is occasionally buggy, counterintuitive and frustrating. It took several stabs before I was able to transfer my Apple Address Book contacts into Google Voice. On occasion, the play button for my voice mail wasn't to be found. And my custom greetings didn't always match the ones listed, a quirk whose potential for disaster was underscored when my boss received the message intended for my friend.

A particularly big problem for me is that I own an iPhone (me and an estimated 6.4 million others in the United States). Unlike a smart phone running on Google's Android operating system or a BlackBerry, there isn't a Google Voice app available for the device. Apple Inc. rejected the one created by Google and removed those created by others, citing duplicative features.

That's not Google's fault, but it is Google's problem. Receiving Voice calls or checking messages from my iPhone isn't more difficult than doing so through my carrier, but I can only manage the service and initiate calls over the browser. That's often more clicks and downloading delays than I'm patient enough to handle.

Additional steps

A similar problem occurs at my desk. Making a call there requires surfing to Google Voice and keying in the number or clicking it in my contacts, additional steps I'm loath to take on busy days - or at least a new habit I haven't yet managed to form.

What this means is that my friends, family and work contacts receive calls from different numbers on different days. And that means they return calls and leave messages at various places at various times.

So much for having all my voice mails in a central spot, remembering a single password, learning one set of phone functions, or managing a lone contact list. Instead, I have yet another layer to manage, on top of my work and cell phones, work and personal e-mail accounts, and Facebook and Twitter feeds.

As with each of these things, I've signed up because Google Voice provides cool new ways of sharing and receiving information. But also with each of these things, I'm left with the feeling that communicating is becoming more work, not less.